Molecular engineering of microporous crystals: (V) Investigation of the structure-directing ability of piperazine in forming two layered aluminophosphates

Molecular engineering of microporous crystals: (VI) Structure-directing effect in the crystallization process of layered aluminophosphates

“…1 suggest that a large amount of crystalline monohydrated piperazinium hydrogenphosphate existed in all of the samples, which can be partially washed away with water during the centrifugation separation process [26]. Before the heating time reached 6 h, a large amount of crystalline piperazinium dihydrogen phosphate existed in the samples, which can be completely and easily washed away with water during the centrifugation separation process [26]. This fact indicates that there is an excess of phosphoric acid and piperazine species in the liquid phase of all of the samples, which do not involve the formation of AP2pip or amorphous aluminophosphate.…”

“…In the initial mixture, the tetrahedral and octahedral Al atoms were confirmed by the appearance of resonance peaks at 47.1 and À10.0 ppm, respectively. In the centrifugation-separated initial mixture, the chemical shift for the octahedral Al is À5.6 ppm [26], suggesting the freeze-drying process slightly changed the local environment of the octahedral Al. The subsequent evolution of the coordination state of Al in the freeze-dried samples is similar to that in the centrifugation-separated samples [26].…”

“…The reaction between piperazine and phosphoric acid leads to the formation of piperazinium hydrogenphosphate or piperazinium dihydrogen phosphate, which are highly soluble in water [33,34]. In contrast to the centrifugation separation method, monohydrated piperazinium hydrogenphosphate is formed in the initial mixture during the freeze-drying process [26]. Fig.…”

“…Recently, the crystallization processes of aluminophosphate molecular sieves were studied using a new strategy/method and by monitoring the crystallization process with in situ or ex situ characterization techniques [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. However, the understanding of the crystallization process of microporous aluminophosphates and the structure-directing effect of organic additives at the molecular level is still insufficient, and the data are sometimes contradictory [27].…”

N-methyldiethanolamine: A multifunctional structure-directing agent for the synthesis of SAPO and AlPO molecular sieves

“…They found that the concentration of the chemicals can affect the formation of intermediate phase in the crystallization pathway of AlPO-11 [14]. Also the relative ratios of species and crystallization temperature can affect the structure-directing ability of the organic amines, leading to different products [15,16].…”